After it warms up it won't idle below 2,000 rpm

indnrdr · Mar 26, 2012

Just acquired a '75 850 MKIII that has been stored for 30+ years (real low miles). I've dealt with "long storage" issues like stuck forks and stuck caliper pistons and have performed overall renewal maintenance, carb cleaning, fresh oil in every capacity, fresh spark plugs, valve clearance check, etc. Put on new mufflers due to rust sediment in the originals.

Now that I can get a ride on it the engine idles beautifully at the start, like a watch, 900 rpms, but after a little expressway riding the idle increases and hovers at 2,000 rpm and won't come down by goosing the throttle. And the engine is hotter than it should be after a short run. Blued pipes attest to that.

Have checked for the lean mixture issues like gasket or cross-over tube air leaks, none so far. I adjusted the slides and did syncronization, they were already pretty close to manual recommendations. I found compromized o-rings at the throttle stop screws and pilot air screws and replaced those.

The pilot air screw adjustments don't seem to make much of a difference in or out.

I plan to go back in and see what idle jets it came with.

And I need to check timing, although it runs and sounds like a Commando should at low and high speeds.

Has anyone experienced the "runs hot and too fast when hot" phenomena?

INDNRDR (Indian Rider...my other ride from 1946).

DogT · Mar 26, 2012

http://www.jba.bc.ca/Bushmans%20Carb%20Tuning.html

Dave
69S

indnrdr · Mar 26, 2012

Thank you. Will go to school on that site tonight.

But a quick read, while having excellent advice about cleaning the air and gas passages, and adjusting the slides and floats, doesn't directly clue me in on why heat makes a difference in holding my idle up at 2,000 rpm.

A lean mixture will cause heat, but what about heat causes the high idle in the meantime?

pete.v · Mar 26, 2012

Get some carb cleaner, compressed air and a number 78 drill bit. Your need to dismantle the carb to get to the bottom of the carb body where the pilot circuit enter the float bowl. Take the drill and epoxy it onto a Q-tip stick. Pull the pilot screws out and clear the pilot jet with the drill. The need for the extension will become clear here.
After studying the diagram at the site Dogt sent you to, blow the cleaner in and clear it with air. Hold your finger over the holes one at a time to confirm the cleaner comes out through the circuit. That ought to do it.

Also search "pilot circuit" in the upper right hand corner. Enjoy the novel.

dynodave · Mar 26, 2012

Worn out automatic advances will cause that also. They fail to return to retard condition then cause hi idle. lack of maintenance/lube causes that.

pete.v · Mar 26, 2012

dynodave said:
Worn out automatic advances will cause that also. They fail to return to retard condition then cause hi idle. lack of maintenance/lube causes that.

That makes sense. Gets hot and stars to bind. should be easy to check, pulling the cover and spraying lube and going for a ride to see if it help. If it does help, order parts. If running EI, never mind.

rx7171 · Mar 26, 2012

I see you are in Kansas, which I'll guess is cold this time of year.
I've ridden my bike all winter when dry and a lot of mornings the temperature is around 40 degrees.
I start with full choke (enricher, Mikuni) and when started have to keep some throttle in to run around 2,000 for several minutes before it warms up a bit or it will die and after taking off needs to run 5-10 minutes for oil to warm enough that I can let it idle down at 1,000 with no throttle.

What I'm getting at is that until warmed up you may be dealing with drag of thickened oil for the first few minutes and when warm the oil allows the idle to pick up to 2,000.

As an experiment when the engine is fully warm dial down the idle to 1,000.
Then let sit overnight, start with lots of choke, nurse throttle to get on road and see if after 5-10 minutes you don't have a nice idle at 1,000.

What I'm saying is you just may have the idle set too high and have to adjust start procedure due to cold conditions.

Bob

bill · Mar 26, 2012

+1 on the auto advance unless it has been converted to an electronic ign.

dynodave said:
Worn out automatic advances will cause that also. They fail to return to retard condition then cause hi idle. lack of maintenance/lube causes that.

Diablouph · Mar 26, 2012

Have you checked to see that the slides are returning to the stop? Doesn't take much to hold them up a little.

Hobot · Mar 26, 2012

Two common things cause hi idle that won't return, the worn out AAU which sticks in full advance and worn Amal throttle slides letting to much mixture pass even closed. Pilot jet not responding can mean float level off but they clog up with zn oxide so must physically clear them with wire or drill size mentioned, solvent will not touch this. Put grease on the Amal slide, like I did to verify that was helped distinctly, then got anodized slides in one number richer to make up for the carb bores also beat up scored. They don't make or repair AAU's. Theres a few out there for 80-120 bux, so most end up with electro ignitions. I vote worn slides your main issue once they warm up and expand. Cdo normal tune should require tickle or choke on every cold start, then just no throttle one kick starts after warmed but can almost always stand a little ticket when in doubt.

lrutt · Mar 27, 2012

I had that problem on my 73. Warms up and 2k idle. Did hte carb clean and still a problem so I ordered a set of the new hard anodized slides from Burlen. Installed and bam, problem went away. They were new enough and just large enough to take up the slop that existed with the old slides. Rock solid idle now for minimal investment.

indnrdr · Mar 27, 2012

pvisseriii said:
Get some carb cleaner, compressed air and a number 78 drill bit. Your need to dismantle the carb to get to the bottom of the carb body where the pilot circuit enter the float bowl. Take the drill and epoxy it onto a Q-tip stick. Pull the pilot screws out and clear the pilot jet with the drill. The need for the extension will become clear here.
After studying the diagram at the site Dogt sent you to, blow the cleaner in and clear it with air. Hold your finger over the holes one at a time to confirm the cleaner comes out through the circuit. That ought to do it.

Also search "pilot circuit" in the upper right hand corner. Enjoy the novel.

During the "revival maintenance" I did following its big sleep I used carb cleaner and compressed air but but didn't think about the drill bit to get any stubborn gunk. Thanks, and thanks for the search tip leading to the novel.

indnrdr · Mar 27, 2012

bill said:
+1 on the auto advance unless it has been converted to an electronic ign.

dynodave said:

Worn out automatic advances will cause that also. They fail to return to retard condition then cause hi idle. lack of maintenance/lube causes that.

Click to expand...

It has the AAU and I suspect the springs are in fact not allowing it to return to retard. The bike had 978 miles on it, seriously. So it has totally original configurations but issues from sitting for 30+ years.

Will check the condition of the AAU as soon as I can. Thanks you guys.

indnrdr · Mar 27, 2012

rx7171 said:
I see you are in Kansas, which I'll guess is cold this time of year.
I've ridden my bike all winter when dry and a lot of mornings the temperature is around 40 degrees.
I start with full choke (enricher, Mikuni) and when started have to keep some throttle in to run around 2,000 for several minutes before it warms up a bit or it will die and after taking off needs to run 5-10 minutes for oil to warm enough that I can let it idle down at 1,000 with no throttle.

What I'm getting at is that until warmed up you may be dealing with drag of thickened oil for the first few minutes and when warm the oil allows the idle to pick up to 2,000.

As an experiment when the engine is fully warm dial down the idle to 1,000.
Then let sit overnight, start with lots of choke, nurse throttle to get on road and see if after 5-10 minutes you don't have a nice idle at 1,000.

The weather report from Kansas is lovey, a balmy 80 degrees today, high 70s for the rest of the week. Thanks for the ideas but it idles sweetly at 900 rpms and only gets hung up when it gets hotter and this spring I haven't really needed the choke to start it, just carb tickling. The heat may be from the AAU, so that's the next thing to check. Thanks again, and come down to Kansas for some sun (and windburn).

What I'm saying is you just may have the idle set too high and have to adjust start procedure due to cold conditions.

Bob

Hobot · Mar 27, 2012

Fuel residue is hardly ever what clogs our carbs its the zn-oxide crustation that requires physical removal methods.
1000 miles ain't enough to eat up AAU pivots and clamping but I have run into springs too loose d/t loosing their tension, or their hook posts worn or bent out taking up the last bit of their pulling back to full retard. If ya decide to go electronic keep me in mind to send the old AAU to. My Trixie had too high idle from both AAU and carb slides worn, so got no joy till new AAU and new slides. I did grease the worn slides after the AAU alone failed to return to 900 idle, so grease them to seal a while to verify that solved the idle return before buying the slides. Idle of course needs to be set with warmed engine and should require a good tickle or choke to start when cool-ish or ends up too rich once warmed up. If ya get hints of back fire starting then back off advance a dash til it just don't, then can measure and index and mark ignition setting. I diddle float level till best idle is gotten with 1.5 air screws out. I use STP thick oil or last time some axle grease in the AAU hoping to extend time to do it again. I've had the float bowl screws get loose or even fall out, which is undetectable at traffic speeds but fails to start well after, or fuel seen pouring out at fill ups and/or then idles too high till resealed.

indnrdr · Mar 27, 2012

hobot said:
Fuel residue is hardly ever what clogs our carbs its the zn-oxide crustation that requires physical removal methods.
1000 miles ain't enough to eat up AAU pivots and clamping but I have run into springs too loose d/t loosing their tension, or their hook posts worn or bent out taking up the last bit of their pulling back to full retard. If ya decide to go electronic keep me in mind to send the old AAU to. My Trixie had too high idle from both AAU and carb slides worn, so got no joy till new AAU and new slides. I did grease the worn slides after the AAU alone failed to return to 900 idle, so grease them to seal a while to verify that solved the idle return before buying the slides. Idle of course needs to be set with warmed engine and should require a good tickle or choke to start when cool-ish or ends up too rich once warmed up. If ya get hints of back fire starting then back off advance a dash til it just don't, then can measure and index and mark ignition setting. I diddle float level till best idle is gotten with 1.5 air screws out. I use STP thick oil or last time some axle grease in the AAU hoping to extend time to do it again. I've had the float bowl screws get loose or even fall out, which is undetectable at traffic speeds but fails to start well after, or fuel seen pouring out at fill ups and/or then idles too high till resealed.

Thanks for the good advice and steps to try. Was in Arkansas last June, Eureka Springs. Pretty country.

DogT · Mar 27, 2012

I used to keep my whole AAU greased up with 'distributor cam lube', it's still available and doesn't fly off easily, but RIG is easier to find, but not as sticky. Just wipe it on everything with your fingers.

Dave
69S

After it warms up it won't idle below 2,000 rpm

Similar threads